Capacitive pressure transducer

Abstract

An integrated semiconductor pressure transducer comprises a central conducting diaphragm located between two frusto-pyramidal recesses defined by contiguous semiconductor body members of conductivity type different from that of the diaphragm. A metal membrane with communicating apertures subtends one cavity and forms a relatively fixed plate of a capacitor, the other plate of which is formed by the diaphragm. A method of making the transducer in semiconductor process steps includes provisions for normal integrated circuit device fabrication whereby a transducer and utilization circuitry are fabricated in the same process into a single integrated semiconductor device.

The invention claimed is: 
     
       1. A capacitive pressure transducer comprising a unitary semiconductor device structure having a relatively flexible central diaphragm portion of enhanced semiconductor material of one conductivity type material and having contiguous diaphragm holding portions of semiconductor material of the opposite conductivity type arranged on opposite sides of said diaphragm portion and having apertures therein also disposed on opposite sides of and extending to said diaphragm portion,   an electric connecting lead from said diaphragm portion to the external side of one of said holding portions,   a metal layer arranged on the external side of said one holding portion over the aperture therein, forming a hollow cavity thereby, and having a plurality of apertures in said metal layer communicating with said hollow cavity,   said metal layer and said diaphragm portion forming a capacitor of variable capacitance due to the flexibility of said diaphragm portion, and   provisions adapting said capacitor for connection into an electric circuit for indicating relative pressure on opposite sides of said diaphragm portion in response to the change of capacitance.   
     
     
       2. A capacitive pressure transducer comprising a unitary semiconductor device structure having a relatively flexible central diaphragm portion of enhanced semiconductor material of one conductivity type silicon material and having contiguous diaphragm silicon holding portions of semiconductor material of the opposite conductivity type arranged on opposite sides of said diaphragm portion and having frusto-pyramidal apertures therein also disposed on opposite sides of and extending to said diaphragm portion,   an electric connecting lead from said diaphragm portion to the external side of one of said holding portions,   an insulating layer arranged over said one side of said holding portion,   a metal layer arranged over said insulating layer on the external side of said one holding portion over the frusto-pyramidal aperture therein, forming a hollow cavity thereby, and having a plurality of relatively smaller apertures in said metal layer communicating with said hollow frusto-pyramidal cavity.   said metal layer and said diaphragm portion forming a capacitor of variable capacitance due to the flexibility of said diaphragm portion, and   electric leads connected to said capacitor portions for connection into an electric circuit for indicating relative pressure on opposite sides of said diaphragm portion in response to the change of capacitance.   
     
     
       3. A capacitive pressure transducer comprising a unitary semiconductor device structure having a pair of body portions of semiconductor material of one conductivity type, each having a frusto-pyramidal aperture therein,   a relatively flexible central diaphragm portion of enhanced semiconductor material of opposite conductivity type,   said body portions being arranged on opposite sides of said diaphragm portion,   an electric connecting lead from said diaphragm portion to the external side of one of said body portions,   a metal layer arranged on the external side of said one body portion over the aperture therein, forming a hollow cavity thereby, and having a plurality of smaller apertures in said metal layer communicating with said hollow cavity,   said metal layer and said diaphragm portion forming a capacitor of variable capacitance due to the flexibility of said diaphragm portion, and   provisions adapting said capacitor for connection into an electric circuit for indicating relative pressure on opposite sides of said diaphragm portion in response to the change of capacitance.   
     
     
       4. A capacitive pressure transducer as defined in claim 1 and wherein said diaphragm portion is of p+ type semiconductor material, and said holding portions are of n type semiconductor material.   
     
     
       5. A capacitive pressure transducer as defined in claim 2, and wherein said holding portions are comprised of monocrystalline silicon and is oriented with the (100) plane parallel to the plane of said diaphragm portions.   
     
     
       6. A capacitive pressure transducer comprising a unitary semiconductor device sandwich structure having a holding layer portion of semiconductor material of one conductivity type having a central aperture therein,   a diaphragm layer portion of enhanced semiconductor material of conductivity type opposite to said one conductivity type and arranged over said holding layer portion,   another holding layer portion of semiconductor material of said one conductivity type having a central aperture therein arranged on the other side of said diaphragm layer portion and having the aperture in alignment with the aperture of the first said holding layer portion,   an insulating layer portion arranged over said other holding layer portion and having at least one aperture therein communicating with the central aperture of said other holding layer portion, and   a metal layer portion arranged over said insulating layer portion and having apertures communicating with said central aperture of said other holding layer portion,   said metal layer and said diaphragm layer portions forming a capacitor of variable capacitance due to the flexibility of said diaphragm layer portion, and   an electric connecting lead from said diaphragm layer portion to an external side of structure for connection into an electric circuit along with an elective connection to said metal layer portion for indicating relative pressure on opposite sides of said diaphragm layer portion in response to change of capacitance.